1. Field of the Invention
This invention relates to fluid communication tubing of the type used in fluid flow sensing elements for measuring fluid flowrates, and more specifically to a manual purge system for periodically cleaning such tubing.
2. Description of the Related Art
As is well-known in the art, fluid communication tubing, or “instrument tubing”, is commonly used to communicate an instrument signal, in the form of a pneumatic pressure signal, between flow elements and pressure transmitters. Such pressure transmitters, or, more accurately, differential pressure transmitters, are commonly available to measure a pneumatic pressure, relative to atmospheric pressure, within a process system as measured by a flow element. The Pitot tube has long been a standard flow measuring element used throughout the process industries. However, in recent years improvements in such a system have been developed, as disclosed and described in U.S. Pat. No. 5,736,651, issued to the present inventor, and incorporated by reference as if fully re-written herein.
Some Pitot tube or Pitot-array flow element applicains involve measurement of particulate-laden air. A problem occurs from the use of such instrument tubing in that the traverse and sensing tubes of the fluid flow sensing elements can become obstructed by particulate within the fluid stream and therefore require frequent cleaning in order to maintain accuracy and consistency. The amount of particulate in the flowing fluid is not always specifically known or measurable, and the decision that there is a need to purge flow sensing elements is not a simple one. The amount of dirt or particulate within the fluid flow stream is difficult to quantify, and can be variable over time and work cycles. One manner of dealing with flow element purging has been to develop complicated and costly automatic purge systems that work on a timed, or other, automatically calculated basis. However, such a system is generally expensive, potentially inappropriate for the particular application, and can lead to an over engineered solution to an intermittent problem.
An alternative to the over-engineered system is the on-site determination to manually purge instrument sensing tubes. Generally, in order to make such a decision, some minimal data input is required, such as an indication of pressure loss or gain in a manner that would indicate to the operator that the sensing tubes have obstructed sensing orifices. However, such a system is usually a make-shift design, and is not upgradable to an automatically timed purge system.
Consequently, a need has been felt for providing an apparatus and method which allows for an inexpensively installed manual purge system that allows the user to determine how often purging is required and, if justified, can be adapted to the use of an automatic purge system.